*{
    margin: 0;
    padding: 0;
    /* box-sizing: border-box; */
}
body{
    /* background-color: #ccc; */
}
header {
    padding: 10px 50px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid #ccc;
}
main{
    display: flex;
}
/* 如果子元素都有flex属性，则子元素的宽度是按照比例来计算的 */
/* 如果某个子元素没有flex属性，另一个子元素有flex属性，则没有flex属性的子元素的宽度是0 */
main aside {
    flex: 1;
    /* width: 30%;
    max-width: 500px; */
}
main > section {
    width: 800px;
    /* flex: 3; */
    /* width: 70%; */
}
@media screen and (max-width: 768px){
    main aside{
        display: none;
    }
}

footer{
    display: flex;
    flex-direction: column;
    justify-content: space-around;
    align-items: center;
    height: 500px;
    background-color: #ccc;
}
footer .box {
    width: 100px;
    height: 100px;
    background-color: #f00;
}